I assume you mean Motorhome when you say RV. Towables are RVs also, if your van was capable of towing there are trailers that sleep that many. as they are designed more toward family
Its possible that if you did find a suitable trailer for rent, that the rental co, owner, or a tow company would relocate it for you at a equal or lesser eventual cost than a Motorhome.
Towables rent for far less than motorized and have all the features.
Another issue to consider is many places have limitations on occupancy, so you might be required to rent 2 sites to accommodate all your group, so maybe a small trailer for sleeping the one family behind the van, a MH for the others. More mobility, no crowd, double the facility.